Add support for new breakpoint column support in VSCode

[Glober777]

Summary of the new feature

VSCode in version 1.39 has got a new feature called Improved UI for column breakpoints:
https://code.visualstudio.com/updates/v1_39#_improved-ui-for-column-breakpoints

According to the release notes, the capability needs to be supported by the underlying runtime/debugger. It would be really handy to be able to set breakpoints in a middle of a one-liner (or for a sub-expression) when working with PowerShell.

[SydneyhSmith]

@globber777 thanks for opening this issue and providing the link to the documentation! I agree that this would be an awesome feature to have but will add the "Up For Grabs" tag since we currently do not have committed time to implement this.

[TylerLeonhardt]

Just to throw down some context...

this is done using the breakpoint locations message in the debug adapter protocol.

In order to support this:

1. Find a way to get PowerShell to return the possible breakpoint locations (preferably via the PowerShell API and not by running a command)
2. Add support for the breakpoint locations message to csharp-language-server-protocol
3. Add a new Handler in PowerShell Editor Services in this directory with the code you discovered in number 1